Oil well pumping apparatus having improved counterbalance means



R. H. DOBBS Oct. 18, 1966 Filed Feb. 21, 1964 5 Sheets-Sheet l :3. 52:225. 7 .1. 2 L @H: P H-HE H:H-HE!E |!ILILIII /04 v I 1M4 1 l i x i R. H. DOBBS Oct. 18, 1966 OIL WELL PUMPING APPARATUS HAVING IMPROVED GOUNTERBALANGE MEANS Filed Feb. 21, 1964 5 Sheets-Sheet 2 sninaHlh -p INVENTOR. P/a/Mfid fi 00/965 R. H. DOBBS Oct. 18, 1966 5 Sheets-Sheet Filed Feb. 21, 1964 INVENTOR. P/a/zara 005K22 m I; 3 9 O1 @wl m J 1/ 1% T m HUMHMHH a W. H w m o -1: hlr A BY 7 ATTORNEY? United States Patent 3,279,266 GIL WELL PUMPING APPARATUS HAVING IMPROVED CUUNTERBALANCE MEANS Richard H. Dobbs, Winfield, Kane, assignor to Harriette E. Hobbs, Winfield, Kans. Filed Feb. 21, 1964, Ser. No. 346,520 12 Claims. (Cl. 74-37) This invention relates to oil well pumping apparatus of the type utilizing a single endless, flexible drive chain for effecting the reciprocation of a polish rod.

The use of a single drive chain in conventional oil well pumping equipment generally requires a slotted crosshead intercoupling the chain and the reversible parts of the equipment, i.e., the polish rod and the counterweight, so that the movements of the parts will be reversed after the same have been shifted in one direction through a. predetermined distance under the influence of the chain. Force is thus exerted on the crosshead by the chain at two different locations for up and down movements thereof and guide structure is required at the ends of the crosshead to keep it from canting inasmuch as a torque is applied to the crosshead as it is moved by the chain.

In structures having a counterweight coupled directly to the drive chain a follower on the chain engages the counterweight to cause it to move with the chain, but the follower slides laterally in the counterweight when the latter is at the upper and lower extremities of its path of travel. Thus, the counterweight itself does not traverse the actual path of travel of the chain, but merely reciprocates vertically. Guides must, therefore, be provided at the sides of the counterweight to limit its movement to a vertical path. The canting problem again arises due to the use of such a counterweight because of the torques applied thereto by the follower. Also, the polish rod cables, the line of action of the weight of the counterweight, and one stretch of the drive chain have never been, to my knowledge, horizontally aligned and parallel with each other during the lifting stroke whereby the prime mover coupled with the drive chain is utilized solely for lifting the polish rod. Therefore, without this specific alignment the prime mover coupled with the drive chain expends work for other purposes than to lift the polish rod.

The present invention provides a pump which is more eflicient than conventional pumping equipment by positioning the aforesaid parts in such a way that the work expended by the prime mover is used solely for lifting the polish rod and none of the work is used to apply torques to any of the parts. By the judicious positioning of the drive chain, the polish rod cable, and the counterweight, all three of these parts are parallel to and horizontally aligned with each other during the lifting cycle of the polish rod so as to completely eliminate all torque loads on the counterweight, for instance.

The instant invention also represents an advance over the state of the art inasmuch as an inclined guide is utilized to bear some of the weight of the counterweight during the lifting of the counterweight as the polish rod descends. Thus, the guide provides a mechanical advantage for the pump and less power is expended by the prime mover as the counterweight is elevated.

It is, therefore, the primary object of the present invention to provide a pump utilizing a single, vertical disposed drive chain and a counterweight coupled directly thereto for movement therewith along its orbital path of travel. By virtue of this construction, the counterweight can be made to move into a position with respect to the chain and a polish rod cable such that the cable, the line of action of the weight of the counterweight and one vertical stretch of the drive chain are in a common vertical plane during the lifting of the polish rod. As a re- 3,279,266 Patented Oct. 18, 1966 sult, a prime mover coupled to the drive chain will be used solely for applying a lifting force to the chain and none of the work expended by the prime mover will be used for other purposes, such as to apply a torque to any of these parts.

Another object of the invention is to provide pumping apparatus of the type described which utilizes a counterweight which can be coupled to the polish rod cable in a way such that the line of action of the weight of the counterweight and the cable are coincident with each other and horizontally aligned with and parallel to a vertical stretch of the drive chain coupled to the counterweight.

Another object of the invention is to provide a pump of the aforesaid character which utilizes inclined guide structure for hearing a portion of the Weight of the counterweight as the latter is shifted upwardly and as the polish rod descends so that less work is required on the part of the prime mover coupled with the drive chain during this movement of the counterweight.

Yet another object of the invention is the provision of a pump which utilizes improved ball joint-type follower means to connect a counterweight to a vertically disposed drive chain so that the counterweight may shift, at least to a limited degree, in a plurality of directions with respect to the chain if such shifting is required.

In the drawings:

FIGURE 1 is a side elevational view of the instant pumping apparatus illustrating one embodiment of the follower connecting the counterweight to a single, vertically disposed drive chain;

FIG. 2 is an end elevational view of the apparatus shown in FIG. 1;

FIG. 3 is a top plan view of the apparatus;

FIG. 4 is a view taken along line 4-4 of FIG. 1;

FIG. 5 is a view taken along line 55 of FIG. 2;

FIG. 6 is an enlarged, cross-sectional view taken along line 6-6 of FIG. 5;

FIG. 7 is a view of the structure of FIG. 6 looking to the right of the same;

FIG. 8 is a view taken along line 8-3 of FIG. 7;

FIG. 9 is a view similar to FIG. 1 but illustrating another embodiment of the follower coupling the counterweight to the drive chain;

FIG. 10 is an enlarged, fragmentary, end view of the apparatus of FIG. 9;

FIG. 11 is a view taken along line 1111 of FIG. 9;

FIG. 12 is an enlarged view taken along line 12--12 of FIG. 9; and

FIG. 13 is an enlarged view taken along line 13-13 of FIG. 9.

The present invention provides oil well pumping apparatus utilizing a single endless, flexible link chain disposed in a vertical plane and having at least one stretch thereof extending along a vertical line. Means is provided for coupling a counterweight directly to one link of the chain so that the counterweight will traverse the actual path of travel of the chain rather than merely reciprocate vertically as in conventional apparatus. The line of action of the weight of the counterweight will, therefore, extend paralel to the vertical stretch of the chain as the coupling means moves therealong.

A flexible cable is adapted to be coupled to a polish rod and to extend at all times in parallelism with the vertical stretch of the chain. When the coupling means moves along the vertical stretch of the chain, the cable, the line of action of the weight of the counterweight, and the vertical stretch all lie in a common plane normal to the plane of the chain. Thus, a vertical lifting force will be applied to the cable and thereby the polish rod as the counterweight moves downwardly along said vertical stretch and, therefore, a prime mover coupled with the drive chain will be utilized solely for lifting the polish rod.

Another significant feature of the present invention is an inclined guide disposed adjacent an inclined stretch of the chain to bear a portion of the weight of the counterweight during the time when the latter moves from its lowest point to its highest point on the chain. The load on the prime mover is thus reduced during this time interval because the guide provides a mechanical advantage for the system.

Ball joint structure is used to couple the counterweight to the drive chain to permit the counterweight to shift in a plurality of different directions when such becomes necessary.

Pumping apparatus shown in FIGS. 1-8, includes an upright support 22 comprised of a number of vertically disposed legs 24 arranged in pairs, extending upwardly from a base 26 and terminating at a rectangular, open frame 28 at the top of support 22.

A pair of plates 30 and 32 are rigid to one pair of legs 24 and are spaced apart to receive a spur gear 34 therebetween rigid to a shaft 36 coupled to a drive pulley 38 adjacent plate 30 as shown in FIG. 1. For purposes of illustration, pulley 38 is of the multiple groove type and has a number of drive belts 40 interconnecting pulley 38 with a suitable prime mover such as a gasoline powered engine.

Plates 30 and 32 also journal a horizontal shaft 42 spaced laterally from shaft 36. A spur gear 44 having a diameter greater than gear 34 is rigid to shaft 42 and in mesh with gear 34. A sprocket 46 rigid to the end of shaft 42 adjacent plate 32 is rotated with gear 44 under the influence of pulley 38.

A pair of plates 48 and 50 rigid to the same pair of legs 24 support a shaft 52 which is journaled thereon and coupled to a sprocket 54 having a diameter larger than the diameter of sprocket 46 as shown in FIG. 5. An endless flexible link chain 56 is coupled with sprockets 46 and 54 for movement in a corresponding direction as pulley 38 is rotated. One stretch 58 of chain 56 is aligned with a true vertical as shown in FIGS. 1 and 5, while the other stretch 59 of chain 56 is inclined relative to stretch 58. Means 60 is provided for releasably maintaining shaft 52 in any one of a number of fixed locations relative to and within aligned slots 62 in plates 48 and 50. Thus, chain 56 can be made to be substantially taut and to remain so at all times.

A follower 64 directly intercouples chain 56 to a counterweight 66 so that the latter will move with the chain and traverse the orbital path of movement of one link thereof. Follower 64 includes a stub shaft 68 having a first socket member 70 integral therewith. Member 70 is provided with a concave surface 72 which is complemental to a sector of a sphere and extends outwardly from the junction of shaft 68 and member 70 in the manner shown in FIG. 8. Member 70 receives a ball 74 having the configuration of a sector of a sphere as shown in FIGS. 7 and 8. Ball 74 complementally engages surface 72 so that it forms a universal joint ball and socket connector with member 70. Ball 74 is coupled with chain 56 by a pair of pins 76 and thus forms a link of chain 56. Chain 56 is flexible at the junction thereof and ball 74 permits chain 56 to pass over and under sprockets 54 and 46 respectively.

A second, annular socket member 80 cooperates with member 70 to releasably retain ball 74 in place. Member 80 is coupled to first socket member 72 by a pair of screws 82 which are threaded into the outermost face of member 70 as shown in FIG. 8. Member 80 is substantially a ring, but has an inner, annular face which is complemental to ball 74 so that the latter may pivot relative to members 70 and 80 but at the same time, be retained thereby. Members 70 and 80 are recessed at areas 84 and 86 respectively, to permit ball 74 to pivot at least through a limited arc about an axis normal to shaft 68 and to the outer face of member 70. Also, opposed regions (not shown) of member 70 adjacent areas 84 and 86 may be recessed to permit ball 74 'to rotate through a limited are about the axis of shaft 68 in either direction.

Counterweight 66 includes a pair of generally rectangular, fiat plates 88 and 90 coupled together in spaced relationship by a central pin 92 and a pair of lower pins 94 and 96. A roller 08 is mounted for rotation on pin 92 and roll-ers and 102 are mounted on pins 94 and 96, respectively. Roller 98 is disposed between a pair of transversely square, upright guides 104 and 106 and rollers 100 and 102 are disposed on opposed sides of guide 106 as shown in FIG. 5. Guides 104 and 106 are coupled with support 22 in a manner hereinafter described and are disposed between plates 88 and 90. Pins 02, 94 and 96 thus retain counterweight 66 shiftably coupled to guides 104 and 106, and rollers 100 and 102 limit the lateral movement of counterweight 66 adjacent its lower extremity, it being clear that rollers 100 and 102 are spaced apart a distance greater than the transverse width of guide 106.

A flat plate member 108, as shown in FIGS. 1, 6 and 7, has a ball bearing 110 coupled with stub shaft 68 to mount follower 64 on a pair of parallel shafts 112 carried by plate 88 and disposed substantially transversely between the side margins thereof. Bearings 114 are mounted in bores through member 108 aligned with shafts 112 to permit sliding action of member 108 longitudinally of shafts 112. When counterweight 66 moves along stretch 59, member 108 shifts along shafts 112 until roller 98 engages and bears against the inner face of guide 104 as shown in FIG. 5. As counterweight 66 moves along stretch 58, member 108 assumes another position relative to shafts 112.

A rigid plate 116 is coupled by fasteners 118 to base 26 to anchor the lower extremities of guides 104 and 106 to support 22. Brackets 120 coupled with the underside of a plate 122 rigid to frame 28 anchors the upper extremities of guides 104 and 106 to support 22. Guide 106 extends along the vertical, whereas guide 104 is inclined with respect to the vertical as shown in FIG. 5. Means may be provided at either extremity of guide 104 to vary the inclination thereof.

A pair of flexible cables 124 and 126 pass througfh aligned holes in plate 122 and are coupled to plates 88 and 90 respectively, at locations 128 therebetween, only one of locations 128 being shown in FIG. 5. Cables 124 and 126 pass upwardly and around a sheave 130 journaled on a shaft 132 carried by a bracket 134 secured to and extending upwardly from frame 28. Cables 124 and 126 extend downwardly from sheave 130 and are coupled with a reciprocating polish rod 136 extending into the casing 138 of an oil well adjacent which base 26 is disposed.

In operation, apparatus 20 is disposed adjacent casing 138, belts 40 are coupled with a suitable prime mover to rotate pulley 38, and cables 124 and 126 are secured to polish rod 136. When the prime mover is actuated, pulley 38 rotates in a counterclockwise sense when viewing FIG. 1 to drive chain 56 so that follower 64 moves downwardly along stretch 58 and upwardly along stretch 59. As follower 64 moves downwardly, counterweight 66 is suspended from chain 56 and the line of action of the weight of counterweight 66 is parallel with stretch 58.

Cables 124 and 126 are maintained substantially parallel to stretch 58 at all times by rollers 100 and 102, and since cables 124 and 126 are symmetrically disposed between plates 88 and 90, the effective tension of cables 124 and 126 is coincident with the aforesaid line of action of the weight. Also, cables 124 and 126, the line of action of the Weight, and stretch 58, all lie in a common vertical plane normal to the vertical plane in which stretches 58 and 59 are disposed. In view of this, effective downward force on cables 124 and 126 is truly vertical and there is no torque applied to counterweight 66 inasmuch as the aforesaid downward force is applied along a line coincident with the line of action of the weight of counterweight 66. Therefore, all of the work expended by the prime mover coupled to belts 40 is used to raise polish rod 136 as counterweight 66 descends along stretch 58 and no work is wasted by the needless application of a torque to counterweight 66. Hence, no guides are required to limit counterweight 66 to a vertical path of travel, as in the prior art.

As follower 64 passes beneath sprocket 46 and then upwardly along stretch 59, member 108 will shift longi tudinally of shaft 112 and plates 88 and 90 will pivot about the point where roller 100 engages guide 106 until roller 98 engages guide 104. A portion of the weight of counterweight 66 will then be borne by guide 104 during upward travel of counterweight 66. This portion can be calculated from the formula:

The ratio, W/F, is defined as the actual mechanical advantage of the system containing counterweight 166 and guide 104. Neglecting friction, this actual mechanical advantage of the system equals the ideal mechanical advantage thereof. Guide 104 thus provides a means for reducing the load on the prime mover as counterweight 66 is elevated.

As follower 64 passes over sprocket 54, member 108 H will shift relative to shafts 112 until plates 88 and 90 are once again directly suspended from follower 64. When this occurs, the line of action of the weight of counterweight 66 will become vertical and move into parallelism With stretch 58.

The use of the ball point connection of follower 64 permits limited movement of chains 56 in a plurality of directions with respect to counterweight 66. This feature permits continued operation of apparatus even though some of the parts begin to wear away and disrupt the original alignments of the parts.

A modification of the invention is illustrated in FIGS. 9-13 and comprises pumping apparatus 220 similar in all respects to apparatus 20 except for the way in which the counterweight is coupled to the chain and the polish rod cables.

An endless flexible drive chain 256 is disposed in a vertical plane and has a pair of stretches 258 and 259, stretch 258 being vertical and stretch 259 being inclined. A follower 264, comprising a ball and socket joint 274 similar in all respects to that described above, connects a counterweight 266 to chain 256 for movement along the orbital path thereof. Follower 264 does not shift laterally of counterweight 266 as does follower 64 of apparatus 20. A stub shaft 268 of follower 264, however, is longitudinally shiftable within a bushing 269 extending through both of plates 288 and 290 comprising counterweight 266 and rotatable relative thereto by virtue of bearings 271. A roller 273 is carried on bushing 269 for rotation relative thereto and for engagement with an inclined guide 304 as counterweight 266 moves upwardly along the inclined stretch 259 of stretch 256.

Follower 264 is secured to counterweight 266 adjacent the upper extremity thereof and centrally disposed with respect to the sides thereof so that, when follower 264 moves downwardly along vertical stretch 258 of chain 256, the line of action of the weight of counterweight 266 will be parallel to stretch 258.

A vertical .guide 306 is cylindrical and is disposed, together with guide 304, between plates 288 and 290. A

sleeve 307 reciprocates along guide 306 and has a pair of loops 328 rigid to and extending laterally therefrom at the upper end thereof. Cables 324 and 326 are secured to loops 328 and pass up to, over and downwardly from a sheave 330 disposed thereabove. Cables 324 and 326 are coupled to the upper end of a polish rod 336.

A lug 342 is rigid to and extends laterally from the lower end of sleeve 307 in alignment with loops 328. Lug

342 has a shaft 344 extending therethrough, shaft 344.

being provided with reduced ends journaled in bearings 348 in plates 288 and 290, respectively. Counterweight 266 is thus pivotally connected to sleeve 307 and thereby coupled with cables 324 and 326. A follower 264 moves downwardly along stretch 258, counterweight 266 will be effectively suspended from chain 256, and the line of action if the weight of counterweight will be parallel to stretch 258. Also, the line of action of the weight, the effective tension of cables 324 and 326 and stretch 258 all lie in a common plane normal to the plane of chain 256. Since plates 288 and 290 are on opposed sides of guides 304 and 306, the line of action of the weight of counterweight 266 will be substantially coincident with the effective tension on cables 324 and 326. There will thus be no torque applied to counterweight 266 as it descends.

The operation of apparatus 220 is the same as that of apparatus 20 except that the lower end of sleeve 307 is forced downwardly by counterweight 266 to in turn pull cables 324 and 326 downwardly. As in apparatus 20, guide 304 bears some of the weight of counterweight 266 as the latter is elevated. By shiftably mounting shaft 268 in bushing 260, counterweight 266 is shiftable to a limited degree laterally of the follower 264. This allows a tolerance for wear on the various moving parts.

The diameter of the upper sprocket coupled to the drive chain is preferably made large, not only to provide an inclined stretch for the drive chain, but to assure a relatively long time lag between the time when the polish rod reaches the bottom of its path of travel and a time when it once again begins to move upwardly. Thus, the polish rod cannot be abruptly jerked upwardly so as to damage or even snap the rod string.

By eliminating torques on the counterweight, I have eliminated the canting problem and thereby the need for guides which prevent canting. My invention is, therefore, much simpler in construction and operation and hence more efficient for substantially continuous, troublefree operation.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In oil well pumping apparatus including a cable attached to a vertically reciprocative polish rod, and a movable, endless drive chain having a first stretch extending along the vertical and a second stretch inclined relative to said first stretch, the combination with said chain and cable of:

a counterweight;

means connecting the counterweight to said chain for movement therewith, said cable being coupled with and extending upwardly from said counterweight, said cable and the line of action of the weight of said counterweight being substantially coplanar with said stretch of the chain as said connecting means moves along said stretch, whereby said counterweight will be utilized solely for applying a substantially rectilinear force to the cable when the connecting means moves downwardly along said stretch; and

an inclined guide adjacent the second stretch of the chain and disposed to partially support said counterweight as the connecting means moves along said second stretch.

2. In oil well pumping apparatus including a cable attached to a vertically reciprocative polish rod, and a movable, endless drive chain having a first stretch extending along the vertical and asecond stretch inclinded relative to said first stretch, the combination with said chain and cable of:

a counterweight;

universal joint means connecting the counterweight to said chain of movement therewith along the path traversed thereby and for movement relative thereto in a number of different directions, said cable being coupled with and extending upwardly from said counterweight, said cable and the line of action of the weight of said counterweight being substantially coplanar with said stretch of the chain as said connecting means moves along said stretch, whereby said counterweight will be utilized solely for applying a substantially rectilinear force to the cable when the connecting means moves downwardly along said stretch; and

an inclined guide adjacent the second stretch of the chain and disposed to partially support said counterweight as the connecting means moves along said second stretch.

3. In oil well pumping apparatus as set forth in claim 2, said inclined guide being parallel to said second stretch, said counterweight having antifriction means engaging the inclined guide when the latter supports the counterweight.

4. In oil well pumping apparatus as set forth in claim 3, said counterweight including a pair of interconnected plates, said guide being disposed between said plates, and bearing means carried by said plates for engaging the guide as the latter supports the counterweight.

5. In oil well pumping apparatus including a cable attached to a vertically reciprocative polish rod, and a movable, endless drive chain having a first stretch extending along the vertical and a second stretch inclined relative to said first stretch, the combination with said chain and cable of:

a counterweight having a shaft thereon:

a follower carried by the chain for movement therewith;

means pivotally mounting the follower on said shaft to thereby connect said counterweight with said chain for movement with the latter along its path of travel, said shaft being disposed substantially transversely of said path, said mounting means being slidable along said shaft to permit tilting of the counterweight, said cable being coupled with and extending upwardly from said counterweight, said cable, the line of action of the weight of said counterweight, and said first stretch being disposed in a common plane when said follower moves along said stretch, whereby said counterweight will be utilized solely for applying a substantially rectilinear force to the cable when the follower moves downwardly along said first stretch; and

an inclined guide adjacent the second stretch of the chain and disposed to partially support the counterweight as the latter moves upwardly in a tilted condition along said second stretch under the influence of said follower.

6. In oil well pumping apparatus as set forth in claim 5, and a vertically disposed guide adjacent said first stretch, and means coupling the counterweight to the last-mentioned guide to permit the tilting of the counterweight and to prevent any substantial lateral movement of said counterweight as said follower moves along said first stretch.

7. In oil well pumping apparatus as set forth in claim 5, said counterweight including a pair of spaced plates, said cable being coincident with the line of action of the combined weight of said plates.

8. In oil well pumping apparatus including a cable attached to a vertically reciprocative polish rod, and a movable, endless drive chain having a first stretch extending along the vertical and a second stretch inclined relative to said first stretch, the combination with said chain and cable of:

a counterweight;

a follower carried by said chain and pivotally mounted on said counterweight to connect the latter with said chain for movement therewith along the path traversed thereby;

a sleeve;

means mounting the sleeve for vertical reciprocation, said cable being secured to and extending upwardly from said sleeve;

means pivotally coupling the counterweight to said sleeve, said cable, the line of action of the weight of said counterweight and said first stretch being disposed in a common plane when said follower moves along said first stretch, whereby said counterweight will be utilized solely for applying a substantially rectilinear force to the cable when the follower moves downwardly along said first stretch.

9. In oil well pumping apparatus as set forth in claim 8, and an inclined guide adjacent to and extending along said second stretch, said guide being disposed for partially supporting the counterweight when said follower moves along said second stretch.

10. In oil well pumping apparatus as set forth in claim 8, said cable being connected to said sleeve at the upper end thereof, said coupling means being secured to the lower end of the sleeve, the upper end of said sleeve being above the upper extremity of said counterweight.

11. In oil well pumping apparatus as set forth in claim 8, said follower having a shaft, said counterweight having a bushing slidably receiving said shaft, said sleeve mountting means being normally in engagement with said counterweight to prevent lateral movement of the latter away from said follower.

12. In oil well pumping apparatus as set forth in claim 8, said counterweight including a pair of spaced plates, said cable being coincident with the line of action of the combined weight of said plates.

References Cited by the Examiner UNITED STATES PATENTS 1,756,089 4/1930 Hunter 7437 1,970,620 8/1934 Park 7437 2,544,484 3/1951 Blackburn 7437 2,926,000 2/1960 Allen 7437 X 2,977,808 4/1961 Dobbs 7437 FRED C. MATTERN, IR., Primary Examiner.

F. E. BAKER, Assistant Examiner. 

1. IN OIL WELL PUMPING APPARATUS INCLUDING A CABLE ATTACHED TO A VERTICALLY RECIPROCATIVE POLISH ROD, AND A MOVABLE, ENDLESS DRIVE CHAIN HAVING A FIRST STRETCH EXTENDING ALONG THE VERTICAL AND A SECOND STRETCH INCLINED RELATIVE TO SAID FIRST STRETCH, THE COMBINATION WITH SAID CHAIN AND CABLE OF: A COUNTERWEIGHT; MEANS CONNECTING THE COUNTERWEIGHT TO SAID CHAIN FOR MOVEMENT THEREWITH, SAID CABLE BEING COUPLED WITH AND EXTENDING UPWARDLY FROM SAID COUNTERWEIGHT, SAID CABLE AND THE LINE OF ACTION OF THE WEIGHT OF SAID COUNTERWEIGHT BEING SUBSTANTIALLY COPLANAR WITH SAID STRETCH OF THE CHAIN AS SAID CONNECTING MEANS MOVES ALONG SAID STRETCH, WHEREBY SAID COUNTERWEIGHT WILL BE UTILIZED SOLELY FOR APPLYING A SUBSTANTIALLY RECTILINEAR FORCE TO THE CABLE WHEN THE CONNECTING MEANS MOVES DOWNWARDLY ALONG SAID STRETCH; AND AN INCLINED GUIDE ADJACENT THE SECOND STRETCH OF THE CHAIN AND DISPOSED TO PARTIALLY SUPPORT SAID COUNTERWEIGHT AS THE CONNECTING MEANS MOVES ALONG SAID SECOND STRETCH. 